Although Austrian scientist F. Reinitzer successfully synthesized the liquid crystal for the first time in 1888, there was no real development of the liquid crystal industry until about 30 year ago. Due to the many obvious advantages of liquid crystal display materials, such as low driving voltage, micro power consumption, high reliability, being able to display large amounts of information, color display, flicker-free and being able to realize flat-panel display, the liquid crystal monomers and liquid crystal display have undergone great development. So far, the liquid crystal monomers can be synthesized into over 10,000 liquid crystal materials, of which, more than 1,000 liquid crystal materials are commonly and frequently used, and can be classified into different categories by the characteristics of the central bridge bond and ring of the liquid crystal molecule, which mainly include biphenyl liquid crystals, phenylcyclohexane liquid crystals, ester liquid crystals, alkynyl liquid crystal, liquid crystals with difluoromethoxy bridge, ethane liquid crystals and heterocyclic liquid crystals, etc. And liquid crystal display has developed from the small TN or STN black and white screen to the big TN-TFT, VA-TFT, IPS-TFT or PDLC color screen.
Major novel liquid crystal display modes include optical compensated bend (OCB), in-plane switching (IPS), vertical alignment (VA), the axis of symmetry microstructure LCD (ASM), twisted multi-domain liquid crystal display and the like.
The liquid crystal cell of different display mode differs in design, driving method, liquid crystal molecule director and direction of glass substrate; and the liquid crystal molecule director and the direction of glass substrate of the OCB mode and IPS mode are parallel, while the liquid crystal molecule director and the direction of glass substrate of the VA mode and the ASM mode is perpendicular when there is no applied electric field.
For IPS in parallel arrangement, the dielectric anisotropy (Δ∈) of the liquid crystal can be positive or negative.
In VA mode, all molecules of liquid crystal are perpendicular with the direction of glass substrate and parallel with the vertical incident right, when there is no applied electric field. And a good dark state will be displayed when the polaroids are orthogonal, which enables such device to have good contrast ratio, and in this case the dielectric anisotropy (Δ∈) of the liquid crystal must be negative. The optical anisotropy (Δn), the thickness of the liquid crystal cell (d) and the wave length of incident right (λ) of the liquid crystal hardly influence the contrast ratio. Besides, the response time of the VA mode is much shorter than the twisted devices, about half of that of the latter. Under the influence of applied voltage, VA devices will mainly produce the bend deformation of liquid crystal molecules, and ECB devices will produce the splay deformation of liquid crystal molecules and the twisted display devices will produce the twist deformation of the liquid crystal molecules, and their response time will be respectively in reverse proportion to the bend, splay and twist elastic constant. And for most liquid crystals, its bend elastic constant is usually larger than its splay elastic constant, and its splay elastic constant is larger than the twist elastic constant, that is the reason why the response time of VA devices is relatively faster.
In order to further idealize the performance of the display devices, researchers are always devoted to study new liquid crystal compounds, and this contributes to the constant development of the liquid crystal compounds and display devices.
Despite the application of cyclopropyl structure in liquid crystal compounds was reported, the considerable performance deficiencies in the then-reported compounds such as poor structure stability, large viscosity and difficult to synthesize have prevent them from practical application.